1. Field of the Invention
The present invention relates generally to reciprocating piston compressors for compressing fluid, and particularly to a suction leaf plate for the valve assembly of such compressors.
2. Description of the Related Art
Suction leaf plates having slots therein which define the suction leaf valves comprise part of the valve assembly of a reciprocating piston compressor. The suction leaf plate is disposed over an opening of a cylinder, between the cylinder and a valve plate. The suction leaf valve, also known as a reed or xe2x80x9cflapperxe2x80x9d valve, includes a cantilevered head or free end which is forced away from the valve plate to admit fluid into the cylinder through a suction port provided in the valve plate during the intake stroke of a piston in the cylinder.
Suction leaf valves are formed by stamping a slot in a suction leaf plate using a die apparatus, the suction leaf plate made of thin valve steel. Known suction leaf valves are formed by stamping a slot of uniform width in the suction leaf plate, the slot is desirably as narrow as possible to reduce the volume of fluid contained within the slot. If overly large, this volume, commonly called re-expansion volume, reduces the efficiency of the compressor, because the fluid within the volume is repeatedly being compressed and expanded without producing any benefit. Therefore, the narrower the slot between the suction leaf valve and the surrounding portion of the suction leaf plate, the smaller the re-expansion volume.
A problem with such narrow slots is associated with the finishing process of the suction leaf valve, known as xe2x80x9cdeburringxe2x80x9d. During the deburring process, sharp metal burrs around the edges of the slot, which results from the stamping process, are removed by placing the suction leaf plates in a tumbler along with an abrasive media. The tumbler is then rotated such that the abrasive media may enter the slot and frictionally engage the edges around the slot to remove any sharp burrs or sharp edges.
The problem with a suction leaf valve having a uniform slot width is that, because the suction leaf valve may flex to a greater extent near the tip of its free end than at its base portion during tumbling, the abrasive media may more easily enter the slot to finish the edges of the slot toward the head of the suction leaf valve than the edges of the slot toward the base of the suction leaf valve. This results in the edges of the slot around the head of the suction leaf valve becoming over finished, and the edges of the slot around the base of the suction leaf valve remaining under finished.
A problem with over finishing is that the edges of the suction leaf valve and suction leaf plate around the slot include broadly sloping surfaces terminating in sharp knife edges. The sharp knife edges are easily dented or cracked upon contact with one another or other objects prior to installation of the valve, and the crack may propagate across the width of the valve to result in failure of the valve. A problem with under finishing is that the sharp burr edges are not removed. The burr edges, similar to the knife edges, may contact one another or other objects prior to installation of the valve, resulting in cracks or dents which may propagate across the width of the valve and result in valve failure during operation of the compressor.
What is needed is a suction leaf valve defined by a narrow slot around the head portion of the valve to minimize re-expansion volume and which allows abrasive media to uniformly enter therethrough, resulting in a uniform finish around the edges of the suction leaf valve and suction leaf plate.
The present invention provides a suction leaf plate for a reciprocating piston compressor, the suction leaf plate having a slot defining a suction leaf valve therein, the slot having a variable width.
The width of the slot in the suction valve plate may be reduced from a maximum at the base portion of the suction leaf valve to a minimum at the tip of the suction leaf valve. The slot in the suction leaf plate may also be characterized as having a width which narrows toward the tip of the suction leaf valve with increasing chordal distances from a point of maximum flex stress on the suction leaf valve to a plurality of points along an edge of the suction leaf valve.
The slot may further include a cutaway portion in the suction leaf plate defining a discharge gas opening, and the slot may terminate in a pair of cutaway lobes disposed on opposite sides of the base of the suction leaf valve, about which the suction leaf valve may flex. The suction leaf valve may be shaped to include a rounded head portion with a tip disposed opposite the base, and a narrowing waist portion extending laterally across the valve between the head portion and the base.
In addition, the width of the slot may be fine-tuned empirically by first stamping a variable width slot in a suction leaf plate, deburring the suction leaf plate, and inspecting the edges of the slot for burr edges and/or knife edges. If burr edges and/or knife edges are found, the slot is modified such that the width of the slot is narrowed at the location of the knife edges and widened at the location of the burr edges, resulting in a modified slot where the edges of the suction leaf valve and suction leaf plate after deburring having a substantially uniform finish, without burr edges and/or knife edges.
In one form thereof, the present invention provides a reciprocating piston compressor, including a crankcase having a cylinder, the cylinder having an opening in an exterior surface of the crankcase; a piston reciprocatingly disposed in the cylinder; a valve assembly including a suction leaf plate, the suction leaf plate covering the cylinder opening; and a suction leaf valve defined by a slot in the suction leaf plate, the suction leaf valve including a base integral with the suction leaf plate, and a tip opposite the base, the slot having a width is reduced from a maximum distance at the base to a minimum distance at the tip.
In another form thereof, the present invention provides a reciprocating piston compressor, including a crankcase having a cylinder with an opening in an exterior surface of the crankcase; a piston reciprocatingly disposed in the cylinder; a valve assembly mounted to the crankcase exterior surface and covering the cylinder opening, the valve assembly including a suction leaf plate; a suction leaf valve defined by a slot in the suction leaf plate, the suction leaf valve having a base portion integral with the suction leaf plate about which the suction leaf valve may flex, and a head portion including a tip located opposite the base portion; a point of maximum flex stress disposed along an edge of the suction leaf valve, the edge defined by the slot; and the slot having a varying width which narrows toward the tip with increasing chordal distances from the point of maximum flex stress to a plurality of points along the edge.
In a further form thereof, the present invention provides a method for manufacturing a reciprocating piston compressor having a crankcase and a cylinder assembly with a cylinder opening, including the steps of providing a suction leaf plate; producing in the suction leaf plate a slot defining a suction leaf valve, the suction leaf valve including a base integral with the suction leaf plate and a tip opposite the base, the slot having a width reducing from a maximum at the base to a minimum at the tip, the slot further defining edges on the suction leaf valve and the suction leaf plate around the slot; tumbling the suction leaf plate in an abrasive media to produce a substantially uniform finish around the edges; and attaching the suction leaf plate to the crankcase and the cylinder assembly to cover the cylinder opening.
In a still further form thereof, the present invention provides a method for manufacturing a suction leaf plate for a reciprocating piston compressor, including the steps of providing a steel plate; producing a slot in the steel plate to form a suction leaf plate, the slot defining a suction leaf valve having a base integral with the suction leaf plate, a tip opposite the base, and edges on the suction leaf valve and the suction leaf plate around the slot, the slot having a width narrowing from a maximum at the base to a minimum at the tip; and tumbling the suction leaf plate in abrasive media to produce a substantially uniform finish around the edges.
An advantage of the present invention is that the width of the slot is relatively narrow around the head portion of the valve to minimize re-expansion volume, yet is relatively wider around the base portion of the valve to permit proper finishing, such that the edges of the suction leaf valve and suction leaf plate have a substantially uniform finish.